Linear accelerometers are commonly used as components of inertial reference systems for airborne, shipboard and drilling applications. The role of a linear accelerometer in such a system is to provide a signal representing accelerations or velocity changes along an axis, which signal is typically input into a system computer. One widely used accelerometer produces an analog current signal that is proportional to linear acceleration along the accelerometer's sensitive axis. To be usable by the system computer, such an analog acceleration signal must be digitized and preferably integrated to produce a digital signal representing velocity changes. Synchronous operation of the accelerometer/digitizer combination is required because the data collection, correction, and navigation computations are done in real time, and no data can be lost as would be the case if a high-speed A/D converter was used.
Prior accelerometer/digitizer designs have used a separately housed analog accelerometer connected by an electrical cable to a circuit board containing the digitizer. Complete inertial reference systems include three such analog accelerometers and three such circuit boards. Since both the analog accelerometers and the digitizers are sensitive to temperature, the control and prediction of temperature gradients under all possible environmental conditions for such systems can be quite difficult. Although the accelerometer and the digitizer can be separately calibrated with respect to temperature, trimming is invariably required when the components are assembled into a complete system. In addition, the space, weight and power requirements of analog accelerometers and digitizers are considerable, and are important considerations in airborne applications. In spite of the above, prior accelerometers and digitizers have not generally been combined in a single, closed housing, in part because of the inflexibility that would result from such an arrangement. For example, most accelerometer/digitizer designs have a certain dynamic range which can be modified only by changing or switching one or more electronic components. Thus, an accelerometer/digitizer design, with prior components, would be incapable of serving in both high acceleration applications, such as missle guidance systems, and low acceleration applications such as space applications.